The present invention relates a resin cylinder head cover of an internal combustion engine.
Apparatuses for adjusting valve timing using a variable valve actuation mechanism are known in the art (for example, Japanese Patent No. 3525709). Such an apparatus includes a hydraulically operated variable valve actuation mechanism provided at a timing sprocket or a timing pulley of an internal combustion engine, and hydraulic pressure supplying oil passages formed in the camshaft. The apparatus uses an oil control valve for driving the variable valve actuation mechanism through the hydraulic pressure supplying oil passages.
In such an apparatus, a valve case is attached to insertion holes formed in the upper portion of the cylinder head cover. The oil control valve is inserted in and secured to the valve case. To supply oil to the oil control valve through the cylinder head cover, metal pipes are provided on the outer surface or the inner surface of the cylinder head cover to define oil passages. A union bolt is attached to each end of each metal pipe, so that the oil passages of the cylinder head cover, which are at the oil supplying side; are connected to the oil passages at the side of the oil control valve.
Since the oil passages of the metal cylinder head cover are defined by metal pipes in Japanese Patent No. 3525709, the metal pipes need to be supported in a raised state from the surface of the cylinder head cover by using union bolts, oil joints, and other supporting members.
This increases the number of metal components and thus increases the weight. Further, resonance due to the operation of the internal combustion engine is likely to degrade the oil sealing performance of the union bolts and the oil joints.
To reduce the weight and the noise level, the use of resin for forming cylinder head covers have been studied. However, as described above, if metal pipes are used for oil passages, the use of resin cannot solve the problems of increase in the number of components and deterioration of the oil sealing performance.